Reland "Mojo C++ bindings: support sync methods - part 2"

mojo/public/cpp/bindings/lib/sync_handle_watcher.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/public/cpp/bindings/lib/sync_handle_watcher.h"
+
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/stl_util.h"
+#include "base/threading/thread_local.h"
+#include "mojo/public/c/system/core.h"
+
+namespace mojo {
+namespace internal {
+namespace {
+
+base::LazyInstance<base::ThreadLocalPointer<SyncHandleWatcher>>
+    g_current_sync_handle_watcher = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+// static
+SyncHandleWatcher* SyncHandleWatcher::current() {
+  SyncHandleWatcher* result = g_current_sync_handle_watcher.Pointer()->Get();
+  if (!result) {
+    // This object will be destroyed when the current message loop goes away.
+    result = new SyncHandleWatcher();
+    DCHECK_EQ(result, g_current_sync_handle_watcher.Pointer()->Get());
+  }
+  return result;
+}
+
+bool SyncHandleWatcher::RegisterHandle(const Handle& handle,
+                                       MojoHandleSignals handle_signals,
+                                       const HandleCallback& callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  if (ContainsKey(handles_, handle))
+    return false;
+
+  MojoResult result = MojoAddHandle(wait_set_handle_.get().value(),
+                                    handle.value(), handle_signals);
+  if (result != MOJO_RESULT_OK)
+    return false;
+
+  handles_[handle] = callback;
+  return true;
+}
+
+void SyncHandleWatcher::UnregisterHandle(const Handle& handle) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(ContainsKey(handles_, handle));
+
+  MojoResult result =
+      MojoRemoveHandle(wait_set_handle_.get().value(), handle.value());
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+
+  handles_.erase(handle);
+}
+
+bool SyncHandleWatcher::WatchAllHandles(const bool* should_stop[],
+                                        size_t count) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  MojoResult result;
+  uint32_t num_ready_handles;
+  MojoHandle ready_handle;
+  MojoResult ready_handle_result;
+
+  while (true) {
+    for (size_t i = 0; i < count; ++i)
+      if (*should_stop[i])
+        return true;
+    do {
+      result = Wait(wait_set_handle_.get(), MOJO_HANDLE_SIGNAL_READABLE,
+                    MOJO_DEADLINE_INDEFINITE, nullptr);
+      if (result != MOJO_RESULT_OK)
+        return false;
+
+      // TODO(yzshen): Theoretically it can reduce sync call re-entrancy if we
+      // give priority to the handle that is waiting for sync response.
+      num_ready_handles = 1;
+      result = MojoGetReadyHandles(wait_set_handle_.get().value(),
+                                   &num_ready_handles, &ready_handle,
+                                   &ready_handle_result, nullptr);
+      if (result != MOJO_RESULT_OK && result != MOJO_RESULT_SHOULD_WAIT)
+        return false;
+    } while (result == MOJO_RESULT_SHOULD_WAIT);
+
+    const auto iter = handles_.find(Handle(ready_handle));
+    iter->second.Run(ready_handle_result);
+  };
+
+  return true;
+}
+
+SyncHandleWatcher::SyncHandleWatcher() {
+  MojoHandle handle;
+  MojoResult result = MojoCreateWaitSet(&handle);
+  CHECK_EQ(MOJO_RESULT_OK, result);
+  wait_set_handle_.reset(Handle(handle));
+  CHECK(wait_set_handle_.is_valid());
+
+  DCHECK(!g_current_sync_handle_watcher.Pointer()->Get());
+  g_current_sync_handle_watcher.Pointer()->Set(this);
+
+  base::MessageLoop::current()->AddDestructionObserver(this);
+}
+
+SyncHandleWatcher::~SyncHandleWatcher() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(handles_.empty());
+  g_current_sync_handle_watcher.Pointer()->Set(nullptr);
+}
+
+void SyncHandleWatcher::WillDestroyCurrentMessageLoop() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_EQ(this, g_current_sync_handle_watcher.Pointer()->Get());
+
+  base::MessageLoop::current()->RemoveDestructionObserver(this);
+  delete this;
+}
+
+}  // namespace internal
+}  // namespace mojo